Help - How am I doing in maths and science?

I'm currently 16, doing second-last year of High School.
For certain reasons, I'm "in the dark" in regard to where I am with my education :P.
It's just like ... when I come here on PF, my breath just gets taken away with the topics and levels of discussion which go on here; makes me kind of worried.

Here's what I'm doing:
Math - Singapore Math (College Math) Volume 1 (Corresponds to second last high school year, I think), done some basic calculus, differentiation and integration.

Science - In the middle of Highschool Physics, after completing Chemistry and Biology. Unfortunately Biology, from 2 years ago, has worked it's way out of my brain, and it's time for review.

I wouldn't worry too much if I were you. Your school's courses should give you enough exposure to each subfields to give a bit of idea what you do in each of them. Hopefully by the time you start applying for universities, you will have a general idea what you like to do. In the first year of two in the university, there will be more introductory type courses, as well as advisers in the departments to help you with deciding what you want to do.

(I am assuming education system in SG isn't too different from commonwealth countries like AU/NZ)

Looks like you are ahead a bit in maths comparing to when I was 16. In terms of science it looks pretty similar. As long as you are comfortable with the current curriculum in your classes, you're fine.